Factitious hypoglycemia due to surreptitious insulin
administration results in elevated serum insulin levels and low or
undetectable C-peptide levels, with a clear reversal of the
physiological molar insulin to C-peptide ratio (≤1) to an
insulin to C-peptide ratio of greater than 1. By contrast, insulin
and C-peptide levels are both elevated in insulinoma and the
insulin to C-peptide molar ratio is 1 or less. Sulfonylurea
ingestion also is associated with preservation of the insulin to
C-peptide molar ratio of 1 or less.

In patients with insulin autoantibodies, the insulin to
C-peptide ratio may be reversed to greater thsn 1, because of the
prolonged half-life of autoantibody-bound insulin.

Dynamic testing may be necessary in the workup of hypoglycemia;
the C-peptide suppression test is most commonly employed. C-peptide
levels are measured following induction of hypoglycemia through
exogenous insulin administration. The test relies on the
demonstration of the lack of suppression of serum C-peptide levels
within 2 hours following insulin-induced hypoglycemia in patients
with insulinoma.

Reference intervals have not been formally verified in-house for
pediatric patients. The published literature indicates that
reference intervals for adult and pediatric patients are
comparable.

Day(s) and Time(s) Performed

Monday through Friday; 5 a.m.-12 a.m., Saturday; 6 a.m.-6
p.m.

Analytic Time

Same day/1 day

Specimen Retention Time

3 months

Test Classification

This test has been cleared or approved by the U.S. Food and Drug
Administration and is used per manufacturer's instructions.
Performance characteristics were verified by Mayo Clinic in a
manner consistent with CLIA requirements.